Hydraulic pumping unit



Jan 12, 1954 R. L. CHENAULT HYDBULLC PUMPING UNIT 4 Sheets-Sheet 1 Filed Deo. 20. 1950 l@ (Inventar 0)/ #Hmz/7, smh m@- Jan. l2, 1954 R. L. cl-IENAUL'T- HYDRAULIC PUMPING UNIT Filed Dec. 20, 1950 [71002150 PW A CHE/mw Jam 12, l954 R. L. CHENAULT HYDRAULIC, PUMRING UNIT Filed Dec. 20. 195.0

ifs #far/rey Jan. 12, 1954 R. l.. CHENAULT HYDRAULIC PUMPING UNIT 4 Shee'tsf-She'et 4 Filed Dec. 20. 195'0 fla/venan /Pay Z. (Hf/mm 7,

i@ @far/zeg Patented Jan. 12, 1954 States ASteel v-vCo'rpc'iration, alcorporationfNew Jersey "Application December 20, 1950, SelialfNo.L 20:1;786

' (ci. A6er-51) y 6v Claims.

lThis invention relatestoimprovements in hydraulic pumping units for operatingv4 subsurface oil well pumps. v

.I am aware thatmany designs o'f `such .units exist and have been patented, but those with which AI am familiar have .disadvantages that have limited their YadoptionV and use.` Fundamentally these units compriseafhydraulic cylinder, -which contains a reciprocable Aram-connected in some way to a-suckerf-rod string, a-motivating' pump for applying hydraulic pressure tol'the cylinder and -thus reciprocating said ram, a valve arrangement for controlling Athe direction in which such pressure is applied and thus controlling reversals of the ram, and acounterbal'- ance for equalizingrthe load on .the motivating pump during vupstrokes vand v-downstrokes of the ram. A suitablevprime mover drives the motivating pump.` yIn most instances positive clis-` placement motivating pumps have been preferred, but such pumps deliver -uidfcontinuouslyand have necessitated complicated Icy-pass l'arrangements `for iluid delivered While `the'ram decelerates and reverses at the ends of its strokes. rlhe counterbalance preferably is pneumaticpbut previous units have failed to utilizethis counterbalanceas a meansffor cushioning the-ram-,fbut only'for storing energy on-thefdownstroke :to assist in theupstroke. In most'previousunitsthe ram has moved at the same speed during bothits upstroke and its downstroke, whereas `advantageously'theram could move much faster during its downstroke.

Centrifugal pumps-and reversible variable volume pumps also-have beenused ais-motivating pumps and'have overcome some of these difficulties, but introduce others. Av centrifugal pump allows slippage during deceleration and reversals of the ram, and thus enables the controls to be'simplied, but such slippage causes a power loss and unduly 'heats the `hydraulic iuid. A reversiblevariable volume pump reduces its delivery to decelerate andl reverse the .ramand it allows fordiierent speeds inthe two strokes. However, such pumps are complicated andicoste ly and they producea Widely fluctuating load on their prime mover.

vAn object of the lpresentinvention `is to provide improved hydraulic pumping units which overcome the foregoing, disadvantages; that is, which employ positive displacementpumps yand yet do not require a complicated byfpass, which utilize their pneumatic counterbalance forcush- `vz `A further .object-ofthe invention is to provide improvedhydraulic pumping units which are capable of absorbing energy continuously from a prime mover-and of-utilizing this energy eiciently for voperating Athe ram without necessity for by-passing,any-hydraulicuid nor decreasing the rate of energyabsorption at the extremes of the ram-stroke.

-A further object ofthe invention is to provide improved .hydraulic pumping-units which employ a positive displacement motivating pumpV and which have ltwo 7pneumaticcounterbalance tanks, the first of saidftanks furnishing pressure which cushions-the ram during its downstroke and superchargesfthe :pump duringthe upstroke ofthe ram, the second of said tanks `furnishing presioning the ram, and in which 'the ra'mjcan move faster during its downstroke lthan fduring'itsupf stroke.

sure-which direotly-assistsV the motivating pump during .the upstroke offthe vram 'and receiving the pump voutput -andvfstoring .its Aenergy during the dovvnstroke.

Inaccomplishing these fand other objects of the: invention, I 4have provided-improved details of structure, lpreferredforms of which are shown in the accompanying drawings, in which:

:Figurel is aschematic vertical sectional view of a hydraulic pumping'unit embodying features of the present invention, :the -v parts -being shown in thefpositions they occupyfor azdownstroke of the ram;

"FigureQis a view similar to .Figure 1, but show'- ing vthe'parts intheir-upstroke positions;

. Figure Bisa schematic vertical sectional view of a unit of the-present invention, but having the valves 'and other details of modified construction, the parts being shown in' their downstroke positions and Figure "elisa schematic vertical sectional view which-shows the valves of Figure 3 in their upstroke positions, other detail'sbeingillustrated as in Figures l land 2forv simplicity. y The 'hydraulic'pumping unit shown in Figures 1V and '2"comprises a lifting cylinder I0, a vram I2 reciprcable up and down in said cylinder, a motivating -piimp I3, a main valve I4, a 'pilot valve I5, 'arstcounterbalance" tank I6, 'and a second'couterbalanctank II'I. vA polishedrod I8 'is' connectedt i'am I2 and -'a sucker' rod string, not'shovvn,1'is` Ciinectedto 'Said polished r'd'and extends into v"a'fvvell casing' VI9'. "This rody string operates a subsurface pump, not shown. `The motivating pump I3 is a positive displacement pump `of any standard or 'desirable' `construction and it' delivers"hydraulicfiuid continuously at substantially constant" volme and' pressure. This lpump is'drivenffroinl'any4suitable prime mvefn't fShWn.

Main valve I4 includes a housing 20 which has three ports 2 I, 22 and 23 and which contains a reciprocable valve spool 24 having upper and lower lands 24a and 24h. A pipe 25 connects port 2l with a port 26 in the lower end of the lifting cylinder I9. A pipe 21 connects port 22 with the inlet side of the motivating pump I3. A pipe 28 connects port 23 with the discharge side of said motivating pump. A pipe 29 connects pipe 21 and the lower end of the first counterbalance tank I3 and contains a throttle valve 30. A pipe 3l connects pipe 28 and the lower end of the second counterbalance tank I1.

The main valve has an operating cylinder 32 which contains a reciprocable piston 33. A piston rod 34 connects piston 33 and the main valve spool 24. A spring 35 surrounds said piston rod and tends to move the piston, piston rod and valve spool to their upper position shown in Figure 1.

A suitable hydraulic fluid fills the lower part of cylinder I0, pipes 25, 21, 28, 29 and 3|, the central part of the main valve cylinder between lands 24a and 24h, and the lower part of counterbalance tanks I6 and I1. The upper parts of these tanks contain compressed air, which initially is supplied from an air compressor 35 and piping 31. This piping contains a pressure regulator 38 which maintains a slightly lower pressure in tank IB than in tank I1. Preferably the tanks have relief valves 39 and 40. The air compressor, pressure regulator and relief valves can be of any standard or desirable construction and hence are not shown in detail. The two tanks are of unequal volume, tank I being the larger, as hereinafter explained.

The lower end of the main valve housing 20 carries an air make-up pump 4i, the purpose of which is to replenish automatically air lost from the counterbalance tanks I6 and I1 through leakage without necessitating operation of compressor 36. This pump includes a cylinder 42, which is fixed to the lower end of said housing, and a plunger 43, which is fixed to the lower face of the main valve spool 24 and thus reciprocates in said cylinder as said valve spool moves up and down. The cylinder has an intake port 44 and a check valve 45 which acts as a discharge port. A pipe 41 connects said discharge port and one of the counterbalance tanks, in this instance I1. On the upstroke of the main valve pool, plunger 43 draws air into cylinder 42 via intake port 44. On the downstroke the plunger forces such air through check valve 45 and pipe 41 into the counterbalance tank.

An adjustable unloading valve 48 is connected between the intake port 44 and pipe 41. Said unloading valve includes a plunger 49 and a spring 50. Normally said spring moves said plunger to a position in which it allows air to enter the intake port. Whenever pressure in the counterbalance tank is sufficient to overcome compression in the spring, it moves the plunger to a position in which it closes the intake port. The pump then ceases to add air to the counterbalance tanks until the pressure drops enough that spring 59 returns the plunger to its normal position. The compression in the spring is adjustable to adjust the pressure maintained in the tanks.

Cylinder I3 has a port 5I in its upper end above ram I2. A low pressure scavenger pipe 52 connects thisv port with the lower end of one of the counterbalance tanks i5 or I1, in this instance I6. Said pipe contains a small scavenger pump 53 of any standard or desirable construccontains a reciprocable valve spool Si having left and right lands Sla and Elb. A pipe 62 connects port 5B and scavenger pipe 52. Cylinder I U has a port 63 in its extreme lower end and a port 64 somewhat above its port 2B. A pipe 65 connects port B3 with both ports 51 and 59 in the pilot valve housing. A pipe S6 connects ports 39 and 64. A pipe 61 connects port 58 with a port 38 in the upper end of the main valve operating cylinder 32.

The pilot valve has an operating cylinder 69 i which has ports 10 and 1I and contains a reciprocable plunger 12. Cylinder I9 has a port 13 in its upper portion. A pipe 14 connects ports I3 and 10. A pipe 15 connects port 1I with pipe 52, which extends to the scavenger pipe 52. Plunger 12 has a stem 16 which extends into the pilot valve housing 55 and is adapted to abut the left end of pilot valve spool 6I. A spring 11 surrounds stem 16 and tends to move the plunger and stem to the left away from the pilot valve spool.

Figure l shows the position of the parts as the ram makes a downstroke. Ram I2 is moving downwardly gravitationally under the weight of the rod string and is situated between ports 13 and 34 of cylinder I0. The space in the pilot valve operating cylinder 39 behind or to the left of plunger 12 is relieved via port 1D, pipe 14, port 13, the upper part of cylinder I9 and port 5I to scavenger pipe 52. Therefore spring 11 has moved plunger 12 all the way to the left. Pilot valve spool 3| has moved all the way to the right, the means for thus moving it being hereinafter described. The left end of land Sla is subjected to pressure from cylinder I9 transmitted via port 64, pipe 63 and port 60. The right end of land SIb is subjected to the same pressure transmitted via port 63, pipe 65 and port 51, so that the spool does not tend to move in either direction. Land Bla blocks port 59 and the spool establishes communication between ports 56 and 58; Therefore the space in the main valve operating cylinder 32 above piston 33 is relieved via port 68, pipe 61, port 5B, pilot valve cylinder 55, port 56, and pipe 62 to scav enger pipe 52. Spring 35 has moved piston 33, piston rod 34, main valve spool 24 and plunger 43 to their upper position. Land 24h of the main valve spool blocks port 23 and the spool establishes communication between ports 2l and 22.

Descent of ram I2 forces hydraulic uid from cylinder IB through port 26, pipe 25, port 2i, main valve cylinder 2D', and port 22, into pipe 21. Part of this fluid flows through pipe 23 and throttle valve 30 into counterbalance tank iii, and part flows into the inlet of the motivating pump I3, which pumps it Via pipes 28 and 3i into tank I1. Thus the air pressure in tank i6 effectively cushions the ram as it descends, and the output of the motivating pump goes to tank I1 where it stores energy to be used later as the pump raises the ram. The adjustment in the opening of throttle. valve, VY30 .aficontrols .-=.the;.fratek 68. The main valve"operatingpiston,V piston-rod and spool and plunger A3 commence to descend against the V`action of. spring '35. The` parts are adjusted so that. the `ram completes itsr downstroke vat the. same Atime the `main :valveA spool reaches its lowerposition.

' Figure r2 shows :the position, 'of the fparts as rthe ram makes anvupstroke. Thezramag'ainis situated between ports 64 and 'i3 of cylinder Ill. As the ram moved-'past port 64, it admitted pressure Ato the-space in .pilot-,valvel cylinder 55 to the left of land 6Ia, :but `spool 6i did=not move since the pressureinthe'space on-the right o1 land 6 I b balanced this pressure'on the left. VLand .24a of the main 'valvefspoo'lblocks'port 22 inthe main valve housing and Athe spool establishes communication between ports 2| and 23.

The fluid from tank 'IznoW-.fiows to the 'inlet of the motivating pump I3 and the pressure in this tank supercharges the pump.'l The duid discharged' from thermotivating pump joinsf fluid forced from tank I1 bythe air .pressure built up therein, and such fluidv iiowsv through the main valve housing,1port'2l,l pipe 25, and port v25 `to raise the ram. The ascent o'f theramfisrmu'ch slowerthan its descent. Y

As the ram approachesthe top of its upstroke, it 'passes port 'I3 in cylinder II),4 whereupon the space inthe Ypilot valve operating cylinder' 69 to the left of its plunger l2 v'is-'subjected `to the pressure of the fluid in cylinder II). 4:Such pressure moves the plunger to the right againstlthe action of spring TI andthe'pressure on the right end of the plungerapplied to a smaller Aarea. The plunger pushes the'pilot` valve spool `ISI to the right and vthus Amov'es'theparts 'to the position for another downstroke "When ram I2 passes port '13 on the nextfdownstroke, the parts have returned fully to the position shown i Figure 1.

Preferably cylinder In and ram I 2V are equipped VWith dashpots to cushion'the'ram' additionally at the ends of itsV strokes. Numerous arrangements are possible, but at the top I have shown a boss 'I8 which `projects downwardly fro'm'the' end of the cylinder and a recess 'I9 in the upper face of the ram. At the bottom' I have shown an annular wall 88 upstan'dinglfrom the bottom of the cylinder andia vboss Btextending downwardly from 'the Aunderside =of therram; 'In accordance with vknown principles, yboth dashpots have `outlet means Whi'chdecrease in area V'as the boss enters `the recess, such as the V-slot 82 shown in the annular Wall 8D.

One of the hazardsof operating'pumping units is that suckerrod strings can break. The pumping unit kpreferably :.is equipped with means-for closing off the pressure "on the rami when there is ya "sudden release of load v caused/by such breakage. Otherwise.A 'the 1 pressure: from the counterbalancetanks :Fandathefmotivating 'pump' ber belowfthe.tdiaphragm'fwith pipei25 fto thefleft ofztheorifice.

r During fthe upstrokegoffthe .'raniwhen the'v rod string i'sisubjectedtoith'e vv'greatest-'stressjhydraulicffluld:ovvsthrough pipe '25 from rglfitto'left so that thef'pressurezto th'eright oorice 84is slightlylfgreater yithan 'fthe pressure to Vvthe tleft. Thereforel fthe pressure f pushing down 'ons ydiae phragm 85 andf tending 'to close valve y83 is slightlywgreater:'than theffpressure 'pushing' up on said diaphragmjand'tending'toopen the'valve. Aspring v8.9 'pushe's'up 'onf theV diaphragm, and at normal''flowage'fthrough pip'e 25 balances this pressure.' differential "so that `valve 83 stays fully open. :lf there is'a'sudden surge offluidthroug'h pipe' 25 caused by a'sudden release of load on the ;ram,` :the pressurev differential across the oriceiincreasesy'overcomes the-force of spring 89 :and partially closes-the' valve, and the ram moves 'slowly tothe top of its cylinder.

.Preferably 'the unit falso is'equippe'd 'with a pressurefswitch 9U for stopping its i'operation Whenithepressure 'dinere'ntialibetween the inlet anddischarge` sides of Jthe motivatingpump I3 becomes toohigh.' This switch is situated in a by-pass line ill,v which is `connected to'pipe's 21 and 28 on opposite Vsides o'ffthe pump. This bypass line serves'm'erely to transmit pressures to the switch; there is no actual Ailovv ofhydraulic fluidthrough it. Whenithe pressure on -the discharge side of 'the pump becomes abnormally high, as for example when valve 83 closes; the pressure' switch `operates and 'stops the prime mover. U

: l previously intentioned, counterbalance Vtank I6 `is 4of larger''volume `than counterbalan'ce tank I1'.l ','Th'e'optimum 'proportions of the volumes 'of theY Itwo 'tanks are determined by the'ratio o'f the =time=required for 'a downstroke to -thatrequire'd'for an upstroke. For example, vif Vthe upstrokere'quires :twice es muchtime asthe downstrokegftank i6 'should have l`twicey the'jvolume off-tank l'I. Then` two-thirds of the hydraulic fluidT which 'ow's from cylinder lu during a downstroke 'flows `to tank I6 and lone-third is pumped into tank I'I by the motivatingpump I3. This :arrangement `insures that' the vlevels of `*hydraulic uid vand 'thev air pressures in the two tanks increase yby @the 'same amount during each downstroke.

` #Figure '3 shows "apumping unit A.which has severa'li` modificati-ons; any of' which' can be'incorporated individually ini-zther'pumping .unit lshown in Iligures .:1-:and2. 'These-modifications fare: a) a""tf'simnlif1ed=inain 'valve whichfelin'iinetesA i-,the operatingrpiston :fand cylinder; :'fbut requires 1a slightly more :complex pilotvalve (b) a 'more sensitive .ilowl control fvalve',` -(c)` Athe addition of an' auxiliary cushioning `tank rwhich vcushions z the Aram during the interval reihe end of its downstr'oke rWhile it still 'isdescendin'g and the main valvefspoolisblocking port 2v2, (d) the `addition of an alternate` outlet pipe fromithe lfirst'counterb'alance tank I 5,' (e) 4the-addition of adjustable connections between'fthe lifting. cylinderand means in the outlet from the 'dashpot at the bottom of the lifting cylinder. Except for these modiiications, the pumping unit is the same as the unit already described, and the same reference characters identify the parts which are the same.

The modied main valve includes a housing 92 and a spool 93, which has two lands 93a and 93h that also function as operating pistons. The housing has ports 2|, 22 and23 similar to the same ports in the embodiment shown in Figures 1 and 2 and similarly connected to the motivating pump |3 and lifting cylinder l0. The housing also has control ports 94 and 95 in its upper and lower ends respectively. Pressure is admitted to the control port 95 to raise the spool to produce a downstroke of the ram and to the control port 94 to lower the spool to produce an upstroke of the ram. In 'each instance the opposite control port is relieved.

The modined pilot valve includes a housing 96 which has eight ports 91, 98, 99, |00, |02, |03 and |04 and which contains a reoiprocable spool |05. Said spool has three lands |0511., |052) and |c, Ports |0| and |04 at the ends of the housing are connected to the lifting cylinder for controlling shifting of the spool in the same fashion as the corresponding ports 51 and 60 in the embodiment shown in Figures 1 and 2. 'I'he modified pilot valve also has the same operating piston and cylinder as this other embodiment. A pipe |06 connects both ports 91 and |00 with pipe 21, which extends between the main valve and the inlet of the motivating pump i3. A pipe |01 connects both ports 98 and 99 with pipe 28, which extends between the main valve and the discharge of said motivating pump. A pipe |08 connects port |02 with the upper control port 94 of the main valve, Yand similarly a pipe |09 connects port |03 with the lower control port 95 thereof.

Figure 3 shows the main valve and the pilot valve in the positions their spools occupy for a Adownstroke of the ram. The pilot valve spool is at the right. The pilot valve admits hydraulic .I

fluid under pressure from the motivating pump discharge to the space in the main valve housing below land 93h of spool 93. The path of flow is via pipes 28 and |01, ports 98 and |03, pipe l|09 and port 95. space above land 93a of the main valve spool via port B4, pipe |08, ports |02 and |00, and pipes |06 and 21 to the inlet of the motivating pump. Therefore the main valve spool remains in its upper position.

Figure 4 shows the modified main valve and pilot valve in the positions their spools occupy for an upstroke. The pilot valve spool changes its position in the same fashion as in the embodiment shown in Figures 1 and 2, so that there is no need to repeat this description. The pilot valve spool now is at the left, Thepilot valve admits uid under pressure from the motivating pump discharge to the space in the main valve housing above land 93a of spool 93. The path of now is via pipes 28 and |01, ports 99 andl |02, pipe |08 and port 94. The pilot valve also relieves the space below land 93h of the main valve spool Via port 95, pipe |09, ports |03 and 91, and pipes |06 and 21 to the inlet-of the motivating pump. Therefore the main valve spool remains in its lower position.

The modified now control valve differs from that shown in Figures 1 and 2 in that its restrictive orice 84a is situated between the valve and The pilot valve also relieves the f the lifting cylinder I0. Therefore the restrictive effect of the valve combines with that of the orice to produce a greater pressure differential between opposite faces of the diaphragm, and causes an immediate closing of the valve when there is any undue increase in the rate of ow.

The modied unit includes an auxiliary tank ||0 which is shown in Figure 3 only. This tank is connected to pipe 25 via an adjustable throttling valve I2 and to the counterbalance tank It via a pipe |13. The latter pipe contains a check lvalve |14 which admits air from the counterbalance tank to the auxiliary tank,but not the reverse. The auxiliary tank carries volume adjustment chambers |5 and I |5a, which are connected to it through adjustable valves ||6 and H611. Valves ||6 and ||6c can be opened or closed to adjust the eiective volume of the auxiliary tank as desired. The lower part of the auxiliary tank contains hydraulic iluid and the upper part compressed air. The latter enters through pipe ||3 and check valve H4 and its pressure always is at least as great as that in counterbalance tank i6. It is seen that Awhen the main valve spool 93 moves downwardly at the bottom reversal of the ram, its land 93a momentarily blocks port 22 while the ram still is descending. Blocking this port cuts off counterbalance tank i5 from the ram, but now the auxiliary tank H0 furnishes sufficient cushioning effect to decelerate the ram smoothly. The throttling valve H2 can be adjusted to control this cushioning eiect. During the upstroke the accumulated pressure in the auxiliary tank further assists the motivating pump in raising the ram.

The modied unit has an alternate outlet pipe ill', which also is shown in Figure 3 only. This pipe extends from the rst counterbalance tank i6 to pipe 21 and contains a check valve i i8. During the downstroke this check valve closes and all now into the counterbalance tank is via y throttling valve 30, as in the embodiment shown in Figures l and 2. During the upstroke the alternate outlet pipe and check valve permit a substantially unrestricted flow of iluid from counterbalance tank I6 to the inlet of the motivating pump |3.

In addition to the regular ports 64 and 13 in the lifting cylinder |0, to which pipes 60 and 1li leading to the pilot valve are connected, the modified unit can have auxiliary ports H9 and |20, which are shown in Figure 3 only. Pipes 6B and 'i0 also are connected to these auxiliary ports, and are valved at their connections to each port. By proper adjustment of the valves, the reversal points of the ram can be varied as desired.

The annular wall at the bottom of the lifting cylinder I0 has two valved outlet pipes |2| and |22 which are shown in Figure 3 only. These pipes join and extend up to a higher point in said cylinder. The valves in these pipes furnish a means for adjusting the flow from inside the dashpot and thereby further controlling the cushioning at the bottom of the downstroke.

From the foregoing description it is seen that the present invention furnishes a relatively simple hydraulic pumping unit which effectively overcomes the difficulties of previous units. The unit employs the more desirable positive displacement type of motivating pump, and yet requires no lay-pass and it utilizes the pump output efcientlyat all times` The counterbalance tanks effectively cushion the ram, as well as storing energy. The basic unit shown in Figures l and 2 is fully eective in these respects, but any of the 9 refinements embodied inthe`modi1ied-"'unitl shown in Figures 3 and 4 can be incorporated-as` desired.

While I have shown and described certainpreferred embodiments of the invention, it is apparent that modifications mayfarise. Therefore, I do not wish to be limited to thedisclosureeset forth 4but only by the scope ofthe appended claims.

I claim:

1. A hydraulic pumping unit' conflprisinga` lifting cylinder,a ram Vmounted for up and down movement in said cylinder and adapted-to be connected to a sucker rod string, a positive;y placementmotivating pump having an inletand a discharge, a main valve, piping connecting-*said inlet and discharge with said main valve and said main valve with the lower portion of said cylinder and adapted to contain hydraulicV duid, a pilot valve for shiftingsaid main 'valve and thus alternately establishing communicationl between said pump discharge and. said cylinder -for admitting hydraulic fluid to the latter for raising said ram, and establishing communication between said cylinder and said pump inlet for allowing said rain to descend gravitationally at a faster rate than said pump raises it, a rst counterbalance tank connected to said piping between said main valve and said pump inlet, a second counterbalance tank of smaller volume than said rst tank connected to said piping between said pump discharge and said main valve, the volumes of said tanks being in substantially the same ratio as the speed of the ram on its descent and its ascent said tanks being adapted to contain hydraulic iluid and compressed air, said iirst tank receiving hydraulic iiuid from said cylinder and cushioning said ram as it descends and supercharging said pump as it raises the ram, said second tank receiving fluid from said pump and storing its energy as the' ram descends and assisting said pump in raising the ram, and means controlling the rate at which uid can flow into said rst tank for controlling the rate of descent of said ram.

2. A hydraulic pumping unit comprising a lifting cylinder, a ram mounted for up and down movement in said cylinder and adapted to be connected to a sucker rod string, a positive displacement motivating pump having an inlet and a discharge, valve means, piping connecting said inlet and discharge with said valve means and said Valve means with said cylinder and adapted to contain hydraulic fluid, said valve means alternately establishing communication between said pump discharge and said cylinder for admitting iluid to the latter for raising said ram, and establishing communication between said cylinder and said pump inlet for allowing said ram to descend gravitationally at a faster rate than said pump raises it, a first counterbalance tank connected to said piping between said valve means and said pump inlet, a second counterbalance tank connected to said piping between said pump discharge and said valve means, said tanks being adapted to contain hydraulic fluid and compressed air, said rst tank receiving hydraulic fluid from said cylinder and cushioning said ram as it descends and supercharging said pump as it raises the ram, said second tank receiving fluid from said pump and storing its energy as the ram descends and assisting said pump in raising the ram, a throttle valve between said piping and said rst tank for controlling the rate at which fluid can flow into said firstv tank for -I controlling the 'frate Iof descent vof said ram, alternate-'outlet means fromy said firstftank to said piping to allowsubstantiallyunrestricted ilow therefrom to said pump while the: tank supercharges the pump,'andf`a-check valve in said 'alternate outlet'means.v

3. A hydraulic pumping unit comprising a lifting cylinden'a'ram vmounted for up and down lmovementinl said cylinder and Va'daptedto be connectedtoa sucker'rodfstring a positive displacement 'motivating pump having an inletV and 'a pump raises it, a rst counterbalance tank connected to said piping between said main valve and said pump inlet, a second counterbalance tank of smaller volume than said ilrst tank connected to said piping between said pump discharge and said main valve, the volumes of said tanks being in substantially the same ratio as the speed of the ram on its descent and its ascent, said tanks being adapted to contain hydraulic fluid and compressed air, the hydraulic lluid from said cylinder on descent of said ram discharging via said main valve and dividing between said ilrst tank and said pump inlet in substantially the same ratio as the volumetric ratio of said tanks, said :drst tank cushioning said ram as it descends and supercharging said pump as it raises the ram, said second tank receiving fluid from said pump and storing its energy as the ram descends and assisting said pump in raising the ram, and a throttle valve between said piping and said rst tank for controlling the rate of descent of the ram.

4. A hydraulic pumping unit comprising a lifting cylinder, a ram mounted for up and down movement in said cylinder and4 adapted to be connected to a sucker rod string, a motivating pump having an inlet and a discharge, a main valve, piping connecting both said inlet and said discharge with said main valve and said main Valve with the lower portion of said cylinder and adapted to contain hydraulic fluid, means for shifting said main valve when said ram approaches the ends of its strokes whereby this valve alternately establishes communication between said pump discharge and said cylinder for raising said ram, and between said cylinder and said pump inlet for allowing said ram to descend gravitationally at a rate faster than said pump raises it, and a pair of counterbalance tanks connected to the piping on opposite sides of said pump, the tank on the inlet side being of greater volume than that on the discharge side and the volumetric ratio of the two tanks being substantially equivalent to the speed ratio of the ram on its downstroke and upstroke.

5. A hydraulic pumping unit comprising a lifting cylinder, a ram mounted for up and down movement in said cylinder and adapted to be connected to a sucker rod string, a motivating pump having an inlet and a discharge, a main valve, piping connecting both said inlet and said discharge with said main valve and said main 11 valve with the lower portion of said cylinder and adapted to contain hydraulic fluid, means for shifting said main valve when said ram approaches the ends of its strokes whereby this valve alternately establishes communication between said pump discharge and said cylinder for raising said ram and between said cylinder and said pump inlet for allowing said ram to descend gravitationally at a rate faster than said pump raises it, a counterbalance tank connected to said piping on the inlet side of said pump adapted to deliver uid to said pump on the upstroke of the ram and to receive fluid from said cylinder on the downstroke, a second counterbalance tank connected to said piping on the discharge side of said pump adapted to deliver uid to said cylinder via said main valve on the upstroke and to receive uid from the pump discharge on the downstroke, and means for dividing the uid discharged from said cylinder on the downstroke between said rst named counterbalance tank and the inlet of said pump in the same volumetric l2 ratio as the speed ratio of the ram on its downstroke and upstroke.

6. A pumping unit as dened in claim 5 in which the means which divides the fluid between said rst named counterbalance tank and the inlet of said pump includes a valve for adjusting the opening to the eounterbalance tank.

ROY L. CHENAULT.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 1,467,522 Amsler Sept. 11, 1923 1,787,686 Kerr Jan. 6, 1931 2,103,962 Wineman Dec. 28, 1937 2,141,703A Bays Dec. 27, 1938 2,251,290 Reed Aug. 5, 1941 2,279,057 Reed Apr. 7, 1942 2,347,302 Twyman et al Apr. 25, 1944 2,481,623 Rued Sept. 13, 1949 2,560,441 Holl July 10, 1951 

